Transcript Electrons

Matter &
The Atom
Matter
The term matter describes all of
the physical substances around us
Matter is anything that has mass
and takes up space
The Universe is made up of
matter and energy
*Matter is made up of
atoms.
*An atom is the
smallest whole particle
of matter.
* Sub-Atomic particles
are smaller than atoms
and are the tiny
particles that an atom is
made of.
Atomic Structure
Nucleus
– Protons
– Neutrons
Electrons
Atomic Structure
Electrons
Tiny, very light particles
Have a negative electrical charge (-)
Move around the outside of the nucleus
Atomic Structure
Protons
Much larger and heavier than electrons
Protons have a positive charge (+)
Located in the nucleus of the atom
Atomic Structure
Neutrons
Large and heavy like protons
Neutrons have no electrical charge
Located in the nucleus of the atom
Atomic Structure
How small is an atom?
Since the atom is too small to be seen
even with the most powerful
microscopes, scientists rely upon
models to help us to understand the
atom.
http://www.youtube.com/watch?v=yQ
P4UJhNn0I
Who discovered atoms?
Democritus (460- 360 BC) He came up
with the idea that matter was made up
of small units.
He actually created the term “atom”
J.J. Thompson
In 1897, Thompson thought that the
atom must be made of negative charges
that were stuck in a positively charged
material.
This was called the
plum pudding model.
Rutherford
Shot particles at a thin sheet of
gold foil. He expected the particles
to pass though.
Most did, BUT some were deflected and
bounced back
Realized that the mass of an atom was not
spread out evenly, but rather it was
concentrated and positively charged
Usually given credit for discovering the proton
Early Models of the Atom
Rutherford
Mostly empty space
Small, positive
nucleus
Contained protons
Negative electrons
scattered around the
outside
Early Models of the Atom
Bohr
Electrons move in
definite orbits
around the nucleus
Meaning they follow
a pattern
Modern Model of the Atom
The electron cloud
Sometimes called
the wave model
Spherical cloud of
varying density
Varying density
shows where an
electron is more or
less likely to be
Describing Atoms
Atomic Number = number of
protons
In a neutral atom, the # of protons
= the # of electrons
Atomic Mass= the number of
protons + the number of neutrons
Ions
An atom that carries an electrical charge
is called an ion
If the atom loses electrons, the atom
becomes positively charged (because the
number of positively charged protons will
be more the number of electrons)
If the atom gains electrons, the atom
becomes negatively charged (because
there are more negative charges than
positive)
Ions
The number of protons does not change
in an ion.
The number of neutrons does not
change in an ion.
So, both the atomic number and the
atomic mass remain the same.
Ions
This atom has lost an electron. Now it has
one more proton than electron.
One more proton means one more positive
charge.
This makes the total charge of the atom
POSITIVE.
This atom has gained an electron. Now it has
one less proton than electron.
One less proton means one less positive
charge.
This makes the total charge of the atom
NEGATIVE.
Isotopes
The number of protons for a given atom
never changes.
The number of neutrons can change.
Two atoms with different numbers of
neutrons are called isotopes
Isotopes have the same atomic #
Isotopes have different atomic Mass #’s
Isotopes
Electrons have special rules….
You can’t just shove all of the
electrons into the first orbit of an
electron.
Electrons live in something called
shells or energy levels.
Only so many can be in any certain
shell.
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Nucleus
1st shell
2nd shell
3rd shell
So let’s try it….
How to draw a Lithium atom
First, look at the Periodic Table
Second, determine the number of
protons (Look @ the atomic number)
Then determine the number of
neutrons (Atomic mass – atomic
number)
Then determine the number of
electrons (Look @ the atomic number)
3
Li
Lithium
7
So let’s try it….
Protons = 3
3
+
+ +
-
Li
-
Lithium
7
Electrons = 3
Neutrons = 4
2 in the 1st shell, 1 in the 2nd
shell
(7-3=4)
Lewis Dot Structure
The Lewis Dot
Structure is a bit
different from the
Bohr model.
It only shows the
element symbol and
it’s outer most
electron shell.
-
-
-
+
+ + +
-
-
+ + +
+
-
-
•
• O ••
••
-
How to…
1. Write the symbol.
2. Start on the right
hand side,
working your way
clockwise around
the symbol.
3. Try Lithium
Created by G.Baker
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Your activity…
Using the beans (Lentils are electrons,
Lima Beans are protons, and kidney
beans are neutrons), create a Bohr
model , and then a Lewis dot structure
model of each of the first 20 elements.
After you have created each model,
draw each model on your chart.
Hint to make a chart, use a burrito fold,
then fold the top down by 1 ½ inches.
Unfold, you now
have 3 columns. Label
Created by G.Baker
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